1. FIELD OF THE INVENTION
This invention relates to a method for agglomerating coal particles suspended in water.
2. PRIOR ART
Transporting coal in the form of pulp water of coal particles prepared by mixing coal particles with water has such an advantage, among others, that scattering of coal particles never occurs during the transportation.
In this case, however, the sum of inherent moisture contained in coal particle and adherent moisture attached to coal particles, that is, total moisture content, becomes so high that combustion efficiency becomes poor if coal particles taken from the pulp water are used directly by conventional practice.
Heretofore, it has been the ordinary expendent to agitate the pulp water in the presence of a binder, such as a unhydrophobic oil so that a higher affinity of the binder toward coal particles can be utilized and adherent moisture content of coal particles is replaced with the binder to effect dewatering, while the coal particles bind themselves together and agglomerate to larger sizes by the action of the binder and by agitation.
The agglomeration process proceeds, successively through three major steps, i.e. coagulation step where the coal particles join together merely by weak binding force to small masses, growth step where the small masses take the surrounding coal particles into themselves to form larger masses by a strong binding force, and concentration step where the larger masses turn or swirl in the agitating pulp water stream to take surrounding finer coal particles into themselves and to form compact or high density masses with smooth peripheral surfaces of good dewatering in shapes of small water-adhering area, that is, in the spherical or ellipsoidal shapes, by stronger binding force. The water within the masses is squeezed out therefrom by attainment of the high density state.
Such process has been used not only to improve the dewatering but also to remove ashes or recover fine coal particles from waste water.
One prior example of it is disclosed in Japanese Laid-open patent appllication No. 70076/78, where an oil fraction as the binder is made an aqueous emulsion before it is added to pulp water, and the resulting aqueous emulsion is added to the water pulp and agitated; the pulp water remaining after removal of the resulting coagulates is subjected to at least one more repetition of the addition of the aqueous emulsion and the successive agitating. It is stated therein that the consumption of both binder and energy can be reduced. However, the efficiency of agglomeratation is lowered with decreasing pulp concentration, and thus it is necessary to increase the pulp concentration. However, more increase in pulp concentration leads to more consumption of power for agitating the pulp water. This is a disadvantage of the prior art.